For example, in an optical device such as a telescope, a binocular or a microscope, an ocular lens is used to further enlarge and view a real image formed by an objective lens. It is demanded that such an ocular lens have a sufficient eye relief (the on-axis spacing between the outermost lens surface of the ocular lens on the viewing eye side and the eye point (the position of the viewing eye) for comfortable viewing, as well as that the lens be well corrected for aberrations through a large angle of view. However, it is well known that, in ordinary cases, when the apparent field of view of an ocular lens is increased, it becomes difficult to secure a sufficiently long eye relief, and aberrations of a luminous flux at the periphery of the field of view, particularly field curvature aberration and astigmatism worsen abruptly.
For example, an ocular lens constructed by disposing a negative lens group and a positive lens group on the object side and the viewing eye side, respectively, and by providing a field stop between the negative and positive lens groups has been disclosed (see, for example, Patent Literature 1). In the ocular lens having the construction disclosed in Patent Literature 1, the negative lens group is disposed on the object side to secure a large eye relief. Also, the provision of the negative lens group having a high refractive power enables reducing the Petzval sum; a condition for suitably correcting field curvature aberration is provided. This type of ocular lens is capable of making the Petzval sum smaller and is more advantageous in correcting aberrations including field curvature aberration if the ratio of the focal length of the negative lens group on the object side and the focal length of the positive lens group on the viewing eye side is closer to 1:1.